Let’s hope tomorrow won’t bring a repeat of the ugly attack on Egypt’s national cathedral.

That happened this week, when Christians leaving a funeral service at Cairo’s St. Mark’s Cathedral — the Coptic equivalent of St. Peter’s — were attacked by a mob of Muslims hurling firebombs. Police who arrived late ended up joining in the attack. The funeral itself was for four Copts murdered in an earlier anti-Copt rampage.

President Mohammed Morsi has responded by saying that an attack on the cathedral is “an attack on me personally.” Unfortunately, like so many of Morsi’s comments directed at Western ears (remember his denials of anti-Semitism?), he hasn’t backed up his promises with action.

If the Arab Spring really heralds fundamental change, the definitive sign will be how the new Arab world treats its minorities.

Ironically, Copts and Muslims worked together in the protests that ultimately led to the ouster of Hosni Mubarak. Under Mubarak, Egyptian Christians had seen a similar pattern of attacks without consequences, so they hoped for better.

But the ascent of the Muslim Brotherhood in Egypt’s new government has come with a steady rise in both physical attacks on Copts and arrests of Copts for alleged anti-Muslim crimes. In an unusually strong criticism of the government, Coptic Pope Tawadros II says that in 2,000 years his church “has not been subjected to anything like this even during the darkest ages.”

The Arab world has always looked to Egypt as its leader. What happens next is more than a question of whether one of the world’s oldest Christian communities can survive. It’s a test of the Arab Spring.